Brain stem afferent connections of the amygdala in the rat with special references to a projection from the parabigeminal nucleus: a fluorescent retrograde tracing study |
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Authors: | Usunoff K G Itzev D E Rolfs A Schmitt O Wree A |
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Institution: | (1) Department of Anatomy and Histology, Faculty of Medicine, Medical University, Sofia, 1431, Bulgaria;(2) Institute of Physiology, Bulgarian Academy of Sciences, Sofia, 1113, Bulgaria;(3) Institute of Anatomy, Faculty of Medicine, University of Rostock, P.O. Box 10 08 88, 18055 Rostock, Germany;(4) Department of Neurology, Faculty of Medicine, University of Rostock, P.O. Box 10 08 88, 18055 Rostock, Germany |
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Abstract: | A recently revealed important function of the amygdala (Am) is that it acts as the brain’s “lighthouse”, which constantly
monitors the environment for stimuli which signal a threat to the organism. The data from patients with extensive lesions
of the striate cortex indicate that “unseen” fearful and fear-conditioned faces elicit increased Am responses. Thus, also
extrageniculostriate pathways are involved. A multisynaptic pathway from the retina to the Am via the superior colliculus
(SC) and the pulvinar was recently suggested. We here present data based on retrograde neuronal labeling following injection
of the fluorescent tracer Fluoro-Gold in the rat Am that the parabigeminal nucleus (Pbg) emits a substantial, bilateral projection
to the Am. This small cholinergic nucleus (Ch8 group) in the midbrain tegmentum is a subcortical relay visual center that
is reciprocally connected with the SC. We suggest the existence of a second extrageniculo-striate multisynaptic connection
to Am: retina–SC–Pbg–Am, that might be very effective since all tracts listed above are bilateral. In addition, we present
hodological details on other brainstem afferent connections of the Am, some of which are only recently described, and some
others that still remain equivocal. Following selective injections of Fluoro-Gold in the Am, retrogradely labeled neurons
were observed in parasubthalamic nucleus, peripeduncular nucleus, periaqueductal gray, dopaminergic nuclear complex (substantia
nigra pars lateralis and pars compacta, paranigral, parabrachial pigmented and interfascicular nuclei, rostral and caudal
linear nuclei, retrorubral area), deep mesencephalic nucleus, serotoninergic structures (dorsal, median and pontine raphe
nuclei), laterodorsal and pedunculopontine tegmental nuclei (Ch6 and Ch5 groups), parabrachial nuclear complex, locus coeruleus,
nucleus incertus, ventrolateral pontine tegmentum (A5 group), dorsomedial medulla (nucleus of the solitary tract, A2 group),
ventrolateral medulla (A1/C1 group), and pars caudalis of the spinal trigeminal nucleus. A bilateral labeling of the upper
cervical spinal cord was also observed. |
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Keywords: | Cholinergic Facial emotion Fear Limbic system Visual system |
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